1. Field of the Invention
The present invention relates to a method for controlling the movement of a control piston of an air control valve for a compressed air-operated double diaphragm pump, wherein the control piston is moved between two end positions in a control cylinder having inlet bores and outlet bores for the compressed air.
The present invention further relates to an arrangement for carrying out the method for controlling a compressed air-operated double diaphragm pump.
2. Description of the Related Art
Compressed air-operated diaphragm pumps are particularly suitable for conveying in a problem-free manner very different media, including those which can be conveyed by other pump systems only with difficulties because they are pastes or powders or have abrasive properties. Diaphragm pumps have a very high technical reliability in demanding pump operation. Another advantage of such diaphragm pumps is that they do not have rotating components and require no shaft sealing members and are completely resistant to dry operation. The pump can be controlled in a simple manner by changing the amount of the compressed air supplied for operation without requiring expensive or complicated control drives.
Because of their many advantages compressed air-operated diaphragm pumps are used, for example, in the food industry for conveying tomato paste, animal food, chocolate mass, etc. or in the cosmetic industry for conveying toothpaste or creams. They can also be found in mining operations or in the construction industry for pumping from mines, for drainage, for ore preparation and for conveying gypsum sludges, asbestos cement sludges etc. Of course, the above-mentioned fields of use and media conveyed are only examples.
Among the components which are essential for the technological reliability and for the controllability of the double diaphragm pump is the air control valve which causes the respective chambers of the diaphragm pump to be subjected to compressed air in accordance with the required conveying capacity.
A compressed air-operated double diaphragm pump is known from German Offenlegungsschrift 31 50 967. This double diaphragm pump includes a pump housing with two housing chambers which are arranged next to each other and at a distance from each other. The housing chambers include a diaphragm arrangement and are divided by the latter into a pump chamber and an air chamber. The air chambers of the two housing chambers are directed toward each other and a compressed air reversing unit is arranged between the air chambers. The compressed air reversing unit conducts compressed air to the two air chambers and alternatingly discharges the air chambers, wherein the pump chambers are connected through valve devices with an intake piece and a pressure piece through which the material to be conveyed in the form of paste or powder is taken into the pump chamber due to the diaphragm movements generated by the compressed air or is forced out of the pump chamber. The compressed air reversing unit includes a valve control piston for reversing the air chamber connecting paths.
The valve control piston includes a mechanically operating drive system with a mechanical energy storing means, wherein the latter is actuated by the movement of the diaphragm arrangements. The energy storing means is formed by a compression spring arranged within the valve control piston. The compression spring is mechanically coupled to a spring-biased ball which locks the control piston in a predetermined end position and releases the control piston only when the compression spring has been pretensioned by the diaphragm arrangement to a predetermined potential energy. This construction causes the control system to be moved back and forth between two stable piston positions, so that staying of the reversing unit in an undefined intermediate position which in the past has been found disadvantageous is essentially avoided.
German Auslegeschrift 27 26 674 discloses a compressed gas-operated double diaphragm pump with two diaphragms which each are arranged in a chamber so as to divide the chamber into a drive chamber and a pump chamber. The diaphragms are connected to each other through a rigid coupling which causes a synchronous movement of the two diaphragms. The control valve includes a piston slide member with two ball locks, wherein the piston slide member is mechanically connected to the rigid coupling of the diaphragms. In the end positions of the piston slide member, a drive pressure gas is alternatingly supplied to one or the other drive chamber of the diaphragm pump. The mechanical connection and the mechanical drive between the rigid coupling of the diaphragms and the piston slide member of the control valves mounted in the pump housing is effected by means of a bar spring having a round or a flat cross-section. The bar spring engages in a lateral opening of the rigid coupling of the diaphragm and in an opening of the piston slide member and is pivotally mounted in an opening of a rib in the housing. Because of the short mechanical coupling between the diaphragm coupling and the piston slide member by means of the bar, the control valve can be arranged in the pump housing. The bar spring is dimensioned such that the ball locks are overcome in the end position of the control valve and, thus, a snap switch is formed for the piston slide member.
German Auslegeschrift 1,453,607 describes a hydraulically operated double diaphragm pump with two diaphragms. Each of the diaphragms is arranged in a chamber and divides the chamber into a pump chamber and a drive chamber. The diaphragms are connected to each other through a rigid coupling which causes a synchronous movement of the two diaphragms. The pump is further connected to a control valve constructed as a piston slide member which is mechanically connected to the rigid coupling of the diaphragms, so that, in the end positions of the movement of the diaphragms, a drive liquid is alternatingly conducted into one and then the other of the drive chambers. The mechanical connection between the rigid diaphragm coupling and the control valve is effected by means of an arm fastened to the rigid coupling. The arm is slidingly guided on an actuating rod connected to the piston slide member. A spring is arranged on both sides of the arm, wherein the travel stroke of the springs is dimensioned in such a way that the two springs are continuously in work connection with the arm. The control piston of the control valve includes two ball locks as locking devices which are released when a certain force exerted by the two springs is applied and cause the valve to be reversed.
As a result, a movement of the diaphragm is achieved up to a desired point at which the diaphragm movement is suddenly interrupted and the opposite stroke is initiated.
The above-described double diaphragm pumps have in common that the movement of the valve control piston is mechanically controlled by the diaphragms which are rigidly connected to each other and that by utilizing a potential spring energy a snap-type device is formed which moves the control piston of the valve back and forth between two end positions. However, the control valves also have in common that they are structurally complicated and that, when the pump capacity is very low, the control valve has the tendency to be caught in an intermediate position and that, when the pump capacity is very high, an exact control of the valve is not possible because of a so-called fluttering of the spring mechanism.
It is, therefore, the primary object of the present invention to simplify the control and the control mechanism of the air control valve for a compressed air-operated double diaphragm pump and to control the movement of the control piston without a mechanical coupling to the pump diaphragm, so that a secure and exact reversal of the control valve is ensured even if the pump operates very slowly or with a very high capacity.